OTC Tools OTC 3631 Heavy Duty Logic Probe Circuit Tester. OTC Tools. Multi-functional design allows testing range of 326 volts. Bright red and green LEDs interpret voltage signals such as ground, power, and frequency. Tests fuel injectors, solenoids, presence of serial data, and tach reference signals. Output tests on MAF, Cam, Crank, Hall Effect VRS sensors and more. High impedance input compatible with computer circuits and sensors. Features and Benefits Air bag safe. 12', heavy-duty, twin clip, red coil cord lead. Checks 6-,12-, and 24-volt systems. Ergonomic, slim designed clear handle. Positive contact molded strain relief. Heavy-duty stainless steel probe with insulated shaft. Email for product availability.